This invention relates to a display controller, and is concerned, for example, with an art directed to a display controller for drawing graphic forms on a cathode ray tube display device.
It is conceivable that a display controller may be used for controlling the display of graphic forms on a CRT display device. The display controller comprises a drawing processor having a function almost identical with a microcomputer. The display controller receives a drawing command consisting of a program instruction which relates to a specific graphic form to be drawn. The drawing processor processes the drawing command to form an address signal and data corresponding to the locus of a graphic form to be drawn, namely an address signal and data to be supplied to a refreshing memory for storing an information bit corresponding to a dot assigned on a picture of the CRT display device.
When an arbitrary graphic form is drawn by such a display controller, the graphic form is specified, in most cases, by a combination of a plurality of drawing commands. Accordingly, when the graphic form drawn by the CRT display device is partly corrected, for example, it is necessary to extract the drawing command relating to the particular part.
Now, therefore, the present invention is directed to facilitating implementation and correction of the drawing program by making it possible to detect simply a drawing command which forms a part of the graphic form displayed on the display device under control of the display controller.